Process of used lubricant oil recycling

ABSTRACT

A used lubricant oil recycling process is disclosed in which a used lubricating oil is injected to a delayed coker downstream of the coker furnace whereby the used oil is thermally cracked into hydrocarbon fuel products which are low in metal contaminants, sulfur and nitrogen. The used lubricant can be preheated in an independent heater to avoid a quenching effect of the process stream when added in an amount greater than about 3% by volume based on the entire volume of the feed.

FIELD OF THE INVENTION

The invention relates to a process for reclaiming used lubricating oilsand an economical process of producing a full range of refinery liquidand gaseous products from used lubricants. Specifically, the inventionrelates to converting used lubricating oils into quality hydrocarbonproducts by injecting the used oil as a feed to a delayed cokerdownstream of the coker furnace.

BACKGROUND OF THE INVENTION

Depletion of the world's petroleum reserves and increased concern forthe environment are incentives for refiners to search for methods ofreclaiming used lubricating oils.

The growing concern for environmental protection has promptedCongressional interest in mandating waste recycling laws. Usedlubricating oils are among the wastes of interest. Proposed legislationhas been directed towards implementing management standards for used oilrecycling. The major focus of certain proposals has been to reintroduceused lubricants to the refinery process. Specific proposals includerequiring refiners to recycle a yearly amount of used oil equal to acertain percentage of their total lubricant oil production, reintroducethe used oil into refinery processes for purposes of producing useablepetroleum products and commence a credit system in which lubricantrecyclers create credits for used lubricant recycling by actuallyrecycling the oil through reintroduction to refinery processes or bypurchasing recycling credits from recyclers in order to comply with themandatory recycling percentage.

Even though the recycling of used lubricating oil by reintroduction intothe refinery process has only been proposed, the refiner would benefitfrom the ability to recycle lubricating oils by reintroducing the oilinto the refinery process. However, problems with reintroducing used oilto the refinery process are severalfold. Certain residual materials suchas metals and lubricant additives in the lubricating oils presentserious logistical problems to the refinery process. Problems includelocating a process step which can accept used lubricating oils withoutthe risks of fouling catalysts, contaminating process streams andcausing coking and fouling of the process lines.

One approach would be to re-refine the oils to produce a lubricantstock. However, re-refining the used oils to produce base lubricant oilstocks is not a completely satisfactory approach because the knownprocesses produce large quantities of sludge which present disposalproblems. Morover, purification procedures required to pretreat the usedoil are costly and can change the quality of the base oil resulting in aproduct of low quality.

SUMMARY OF THE INVENTION

In view of the environmental concerns for hazardous liquid wastedisposal methods and the scarcity of fuel reserves, there is a need fortechnology which can convert the waste lubricants into useful liquidhydrocarbon fuels.

It has now been found that a delayed coking process can be used toconvert untreated, used lubricant into lighter, high-quality products.The used lubricants are collected and the hydrocarbons contained in thelubricants are thermally coked or vaporized to produce lighter fuelproducts. In the process, the reclaimed oil is introduced to the heatedcoker feed downstream of the coker furnace at a rate sufficient tomaintain the temperature of the coker process stream at a temperaturesufficient for delayed coking and to prevent premature coking of thefeed. The feedstock is then transmitted to delayed coking drums duringthe normal coking portion of the delayed coking process. Inorganic,non-hydrocarbon contaminants contained in the used oil becomeconcentrated on the coke product and the hydrocarbon constituents arethermally cracked to form liquid hydrocarbon components which are ofhigher value as combustion fuels. The contaminants do not, to anyunacceptable degree, show up in the final liquid product or in refineryemissions. Thus, the lubricant contaminants which are typically metals,sulfur and chlorides do not present the refinery processing problemencountered in known used lubricant reclaiming processes. Anycontaminants are in a form which can be handled by conventional refinerytechniques.

THE DRAWINGS

In the accompanying drawings

FIG. 1 is a simplified schematic representation of a conventionaldelayed coker unit;

FIG. 2 is a schematic representation of the modified delayed coker unitshowing the additional furnace used for preheating the reclaimedlubricant.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a process of used lubricant oil recyclingwhich comprises: feeding the used lubricant into a coker by mixing itwith a coker feedstock heated to an elevated coking temperature in acoker furnace downstream of the coker furnace and carrying out delayedcoking of the feedstock in a coker drum from which the coke and liquidcoker products are removed.

Briefly, the delayed coking process is an established petroleum refineryprocess which is, typically, used on very heavy low value residuum feedsto obtain lower boiling products of greater quality. It can beconsidered a high severity thermal cracking or destructive distillationand is used on residuum feedstocks containing nonvolatile asphalticmaterials which are not suitable for catalytic cracking operationsbecause of their propensity for catalyst fouling or for catalystdeactivation by their content of ash or metals. Coking is generally usedon heavy oils, especially vacuum residua, to make lighter componentsthat can then be processed catalytically to form products of highereconomic value. In the delayed coking process, the heavy oil feedstockis heated rapidly in a tubular furnace to a coking temperature which isusually at least 450° C. (about 840° F.) and, typically 450° C. to 500°C. (about 840° F. to 930° F.). From there it flows directly to a largecoking drum which is maintained under conditions at which coking occurs,generally with temperatures of about 430° C. to 450° C. (about 800° F.to 840° F.) under a slight superatmospheric pressure, typically 5-100psig. In the coking drum, the heated feed thermally decomposes to formcoke and volatile liquid products, i.e., the vaporous products ofcracking which are removed from the top of the drum and passed to afractionator. When the coke drum is full of solid coke, the feed isswitched to another drum and the full drum is cooled by a water quenchand emptied of the coke product. Generally, at least two coking drumsare used so that one drum is being charged while coke is being removedfrom the other.

Typical examples of conventional coker petroleum feedstocks includeresidues from the atmospheric or vacuum distillation of petroleum crudesor the atmospheric distillation of heavy oils, visbroken resids, tarsfrom deasphalting units or combinations of these materials. Typically,these feedstocks are high-boiling hydrocarbons that have an initialboiling point of about 350° F. or higher and an API gravity of about 0°to 20° and a Conradson Carbon Residue content of about 0 to 40 weightpercent.

A conventional delayed coker unit is shown in FIG. 1. The heavy oilfeedstock, usually a warmed vacuum residuum, enters the unit throughconduit 12 which brings the feedstock to the fractionating tower 13,entering the tower below the level of the coker drum effluent. In manyunits the feed also often enters the tower above the level of the cokerdrum effluent. The feed to the coker furnace, comprising fresh feedtogether with the tower bottoms fraction, generally known as recycle, iswithdrawn from the bottom of tower 13 through conduit 14 through whichit passes to furnace 15a where it is brought to a suitable temperaturefor coking to occur in delayed coker drums 16 and 17, with entry to thedrums being controlled by switching valve 18 so as to permit one drum tobe on stream while coke is being removed from the other. The vaporousproducts of the coking process leave the coker drums as overheads andpass into fractionator 13 through conduit 20, entering the lower sectionof the tower below the chimney. Quench line 19 introduces a coolerliquid to the overheads to avoid coking in the coking transfer line 20.

Heavy coker gas oil is withdrawn from fractionator 13 and leaves theunit through conduit 21. Distillate product is withdrawn from the unitthrough conduit 25. Coker wet gas leaves the top of the column throughconduit 31 passing into separator 34 from which unstable naphtha, waterand dry gas are obtained, leaving the unit through conduits 35, 36, and37 with a reflux fraction being returned to the fractionator throughconduit 38.

In the modified delayed coking process of the instant invention, usedlubricants such as automotive lubricating oils, turbine oils, jetlubricants, hydraulic fluids, marine and diesel engine oils, automatictransmission fluids, solvents, and the like and mixtures thereof areused as a co-feed in a delayed coker unit. The used oil is fed to theunit in a highly impure form. Usually, consumers mix different brands ofoil, and even if consumers pay particular attention to consistentlyusing the same brand of oil, manufacturers will change the formulationform time-to-time. Moreover, when the used oils are reclaimed forrecycling or proper disposal, no attention is given to segregating theoil by grade or quality. Therefore, these used lubricating oils,typically, comprise one or more than one base lubricating oil, i.e.,mineral oil or synthetic oil. The lubricating oils also contain avariety of additives which may have reacted with each other or with thebase lubricant to form new compounds. The used oil also containssignificant levels of oxidation by-products, ash, sludge, metals, dirt,etc. Moreover, the base oil can contain different synthetic and mineralbase oil components. Examples of base components of mineral oils are thehigher boiling point fractions of paraffins and naphthenes which boilabove 250° C., typically from 300° C. to 550° C. Examples of the baseoil components of synthetic oils include the polyalpha olefins, estersof dibasic acids, esters of polyols, alkylbenzenes andalkylnaphthalenes, polyalkylene glycols, phosphate esters and silicones.This represents only a few of the possible components which may be foundin a waste lubricant reserves. Although the unknown composition of theseoils would ordinarily present a serious processing dilemma to therefiner, they do not present any serious processing problems to arefiner when processed in accordance with the instant invention.

The following Table 1 presents the estimated metals content of a typicalused lubricating oil:

                  TABLE 1                                                         ______________________________________                                        METALS CONTENT OF TYPICAL                                                     USED LUBRICATING OIL                                                                 Element ppmw                                                           ______________________________________                                               Arsenic 0-5                                                                   Barium  10-50                                                                 Cadmium 0-1                                                                   Chromium                                                                              3-7                                                                   Lead     0-99                                                                 Mercury 0.2                                                                   Selenium                                                                              0                                                                     Silver  0                                                                     Aluminum                                                                              2                                                                     Boron   50                                                                    Copper  100                                                                   Iron    200                                                                   Lithium 2                                                                     Manganese                                                                             10                                                                    Molydenum                                                                             10                                                                    Nickel   0-50                                                                 Phosphorous                                                                           1000                                                                  Silicon 100                                                                   Tin     3                                                                     Vanadium                                                                               3-200                                                                Zinc    1000                                                                  Calcium 1000                                                                  Magnesium                                                                             500                                                                   Potassium                                                                             100                                                                   Sodium  150                                                                   Chlorides                                                                               0-1700                                                       ______________________________________                                    

In the instant process, the waste lubricant does not necessarily requirethe preprocessing or pretreatment steps of distilling, filtering ordecanting to remove metals, sediment and other non-hydrocarbons andcontaminants before admixture with the delayed coking process stream.However, mixing, agitating or stirring the lubricant before introductionto the delayed coker process stream may keep the non-hydrocarbons andother materials dispersed in the lubricant which facilitates processing.

Lubricants are low in coke precurser content. For example, lubricantscontain very few of the asphaltenes, resins and heavy aromatics whichreact to form coke. Thus, used lubricant does not present a potentialsource for coke; however, the paraffin and naphthene content allowsalmost all of the used lubricant to convert to the valuable liquidproducts of the delayed coking process and at almost no extra cost tothe refiner. The metals and other contaminants present in the lubricantdeposit onto any coke produced by the feedstock and do not show-up inthe final liquid product or in refinery emissions to any appreciable orinsurmountable degree.

The used lubricant is introduced directly to the coker drum downstreamof the coker heater at a rate sufficient to maintain the temperature ofthe coker process stream for carrying out delayed coking. Alternatively,the used lubricant is heated through an independent heater or indirectlythrough contact with the hot process stream or a hot slip stream to atemperature of at most about 525° C., preferably 260° C. to 425° C. andinjected into a conventional delayed coker feed whereupon the wastelubricant is transformed to more valuable liquid hydrocarbons which canbe used without further processing or can be processed further toproduce gasoline.

A relatively low rate of introduction is important when the usedlubricant is added to the feed without any preheat step. The rate ofintroduction of the used lubricant is up to 3, no more than 10, butpreferably 3-5, volume percent based on the total volume of the feedwhich should avoid cooling of the coker process stream which wouldresult in fouling in the process lines and premature coking. When morethan about 10 volume percent of the lubricant is introduced to theprocess the preheat step is necessary to avoid the quenching effect ofintroducing cold used lubricant into the hot process stream. The term"quenching" is used to mean the undesirable quick cooling of the cokerfeedstock which causes premature coking of the normal feedstock in thefurnace tubes. Although a solution to the quenching problem might be toraise the coker furnace outlet temperature to maintain the coke drumtemperature, this increases the likelihood of coke formation in thefurnace tubes with a concomitantly greater maintenance requirement toclean the furnace tubes.

The used lubricant is introduced downstream of the coker furnace toeliminate any harmful effects which the metals may have on the furnace,reduce process handling and avoid premature volatilization which caninhibit the product yield or result in premature lubricant degradation.Most particularly, the lubricant is introduced downstream to avoid thedeleterious effect that metals can have on the coker furnace tubes byaccelerating the rate of the coke deposition within the coker furnacetubes which occurs at normal coker furnace temperatures.

The preheating step also serves to partially thermally decompose thewaste lubricant and drive off any water which may be dispersed in thewaste lubricant. However, a flash drum can be used. The heating step,when used, is conducted for a period of time ranging from 0.1 to 3hours, or more. Although not necessary, this step can be conducted underpressure, i.e., about 10 to 400 psi or higher.

The preheated, used lubricant is injected into a conventional feeddownstream from the coker furnace. Thereafter, the entire feed istransmitted to a coker to complete the thermal decomposition. The cokeris maintained at temperatures within the range of from about 400° C. to550° C.

FIG. 2 illustrates a schematic representation of the delayed coking unitof the instant invention in which the independent used lubricant heateris employed. For convenience, most related parts of the unit are giventhe same reference numerals as in FIG. 1. This unit operates in the samemanner as the unit shown in FIG. 1 with respect to the conventionalcoker feedstock. However, the unit comprises an independent heater whichheats the used lubricant to at most about 525° C., more specificallyfrom 260° C. to 425° C. The warmed conventional feedstock enters theunit through conduit 12, which brings the feedstock to the fractionatingtower below the level of the coker drum effluent. The feed to the cokerfurnace, comprising fresh feed together with the recycle, is withdrawnfrom the bottom of tower 13 through conduit 14 through which it passesto furnace 15a where it is brought to a suitable temperature, typicallyranging from about 400° C.-550° C. The used lubricant is brought atatmospheric temperature (about 20° C.) from storage 42 to a supplementalfurnace 15b through conduit 43 and is heated in the independent heaterto a temperature ranging from at most about 525° C. specifically, 260°C.-425° C. The heated used lubricant is injected into the conventionalcoker feed downstream of the coker furnace which is traveling to thedelayed coking drums 16 and 17 through conduit 14. The independentheater is necessary when the used lubricant is injected at an injectionrate ranging from more than about 3%, preferably when the injection rateis greater than from about 3-5%, no more than 10%, by volume of thetotal amount of fresh feed. To correct any small quench on the processstream, the heater 15a outlet temperature is increased slightly about0.1° to 20° C. to maintain coke drum temperatures. In the normal way,entry to the drums is controlled by switching valve 18 so as to permitone drum to be on stream while coke is being removed from the other. Theliquid products of the coking process, the vaporous cracked products,heavy coker gas oil, distillate and coker wet gas can be used as is orcan be further processed, as the case with any conventional cokerproduct.

Stream blowback is used in the process to prevent plugging of theconnection used to route the oil into the furnace effluent transfer lineand to help mix the lubricating oil into the coker feed process stream.The steam can be supplied by conventional sources, it can be processsteam or purchased.

An important aspect of this process is that the undesirable heavy metalsand other undesirable components in the used oil deposit on the coke.These harmful metals are not found in the liquid product to anyprohibitive degree.

The invention is illustrated in the following Example in which allparts, proportions and percentages are by weight unless stated to thecontrary.

EXAMPLE

To illustrate the effect of this process on an existing delayed cokerunit, a test run is performed on a commercial coker feedstock. Thecomposition of furnace feed samples comprise a normal coker feedinjected with a lubricant oil slop which is comparable to a usedlubricating oil. The metals content of the lubricating oil slop is shownin Table 2. For comparative purposes, the metals content of aconventional coker feed is also shown in Table 2. The metals content inboth is evaluated before the test and during the test. In the test run,the used lubricant is injected without preheat and at a relatively lowinjection rate of 1.35% by volume of the total feed. The test isconducted under the steady state conditions as set forth in Table 3. Theprocess is fitted with a 6.5 gpm positive displacement pump capable of150 psig discharge pressure and a local flow meter ranged for 159 B/D.Steam is used to prevent pluggage of the connection and to mix thelubricant into the coker furnace process feed. In the test 18,100gallons of used lubricant are processed using four coke drums over aperiod of about 3 days. For the first two test drums, 500 barrels ofsludge are added to the quench water which is used to cool and removethe coke. No sludge is added to the last two drums.

                  TABLE 2                                                         ______________________________________                                                            COKER                                                              LUBE-OIL-SLOP                                                                            FURNACE FEED                                                       Pre-test                                                                            Test       Pre-test                                                                              Test                                        ______________________________________                                        Arsenic                       NT    NT                                        Barium     2        2         NT    NT                                        Cadmium                       NT    NT                                        Chromium   TR      TR         TR    TR                                        Lead       TR      TR          1     2                                        Mercury                       NT    TR                                        Selenium                      NT    NT                                        Silver     1       TR         TR    TR                                        Aluminum   TR      TR         TR    TR                                        Boron                         TR    TR                                        Copper     5        5         TR    TR                                        Iron       1        1         17    16                                        Lithium                       NT    NT                                        Manganese                     NT    NT                                        Molydenum  TR      TR         TR    TR                                        Nickel     NT      80         NT    58                                        Phosphorus 190     190        TR    TR                                        Silicon    6        3          2     1                                        Tin        TR      TR         TR    TR                                        Vanadium   NT      111        NT    210                                       Zinc       205     216         2     2                                        Calcium    810     760         2     3                                        Magnesium  56       56         2     2                                        Potassium  NT      NT         NT    NT                                        Sodium     TR      TR         NT    17                                        Chlorides  <100    930        NT    NT                                        ______________________________________                                         Legend                                                                        TR = Trace Result                                                             NT = No Test                                                                  Blank = None detected                                                    

                  TABLE 3                                                         ______________________________________                                        PROCESS OPERATING CONDITIONS                                                                    PRE-TEST                                                                              TEST                                                ______________________________________                                        TEMPERATURES (° F.):                                                   B Heater outlet     914       925                                             Drum inlet          880       880                                             Drum vapor line     788       788                                             PRESSURES (psig):                                                             Drum                30        30                                              Heater outlet       52        52                                              Lube pump discharge --        84                                              FLOWS:                                                                        Furnace inlet rate (B/D)                                                                          10340     10340                                           Simulated used lubricant addition                                                                 --        141                                             rate (B/D)                                                                    Volume % of slop oil in total                                                                     --        1.35                                            feed                                                                          ______________________________________                                    

Table 4 presents the results of an analysis of the metals content of thefinal liquid product and the drain water. As shown in Table 4, the testprocess does not appreciably increase the metal concentration of any ofthe liquid products. Comparing the results, although there is a changein the concentration of certain metals as a consequence of the additionof a simulated used lubricant oil to the process stream, the change isinconsequential in comparison to the concentrations detected in thestarting used lubricant oil. Note particularly that vanadium, zinc,calcium salt and magnesium salt are present in the slop in very largequantities, i.e., in parts per million, vanadium=111, zinc=216, calciumsalt=760 and magnesium salt=56. However, relatively low concentrationsof these materials turned up in the liquid products and drain water whencompared to the large concentration contained in the used lubricant oil.As far as any notable increases in concentration, the process removesthe larger proportion of contaminants leaving the instant liquidproducts with manageable levels, whereby the fractions can undergofurther processing in existing refinery equipment to remove theundesirable amounts which remain in the products. From the test results,it is concluded that a waste lubricant feed which contains a largemetals content would produce liquid coker products having acceptablelevels of these metals.

                                      TABLE 4                                     __________________________________________________________________________    PRODUCT ANALYSIS                                                                                                          Drain                             RCRA      LT Gasoline                                                                          HVY Gasoline                                                                         LT Gas Oil                                                                           HVY Gas Oil                                                                          COKE  H2O                               LIMIT     1 11                                                                              111                                                                              1 11                                                                              111                                                                              1 11                                                                              111                                                                              1 11                                                                              111                                                                              1  11 1 11                              __________________________________________________________________________    Arsenic                                                                             5   NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT NT NT                                                                              NT                              Barium                                                                              100               NT  NT NT                                                                              NT                                                                              NT       TR                                                                              TR                              Cadmium                                                                             1                 NT  NT NT                                                                              NT                                                                              NT                                         Chromium                                                                            5            TR   TR                                                                              TR                                                                               1 TR                                                                              TR                                                                              TR                                         Lead  5            TR   TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR                                         Mercury                                                                             0.2 NT                                                                              0 NT NT                                                                              0 NT NT                                                                              TR                                                                              NT NT                                                                              TR                                                                              NT       NT                                                                              TR                              Selenium                                                                            1   NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT  NT NT                                                                              NT                                                                              NT NT NT NT                                                                              NT                              Silver                                                                              5   NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT TR                                                                              TR                                                                               2 TR                                                                              TR                                                                              TR NT NT NT                                                                              NT                              Aluminum  1 3 TR 1 1 TR TR                                                                              TR   TR                                                                              TR                                                                              TR 150                                                                              167                                                                               4                                                                               1                              Boron                TR TR                                                                              TR                                                                              TR TR                                                                              TR                                           Copper    TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR TR TR                                   Iron      2 2 1  2 2 1  TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR 364                                                                              333                                                                              24                                                                               2                              Lithium                 NT  NT NT                                                                              NT                                                                              NT                                         Manganese               NT  NT NT                                                                              NT                                                                              NT       TR                                                                              TR                              Molydenum               TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR                                         Nickel    TR                                                                              TR                                                                              TR TR                                                                              TR   NT                                                                              TR                                                                              NT TR                                                                              2 NT 145                                                                              162                                                                              TR                                                                              TR                              Phosphorus                                                                              NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR       NT                                                                              NT                              Silicon   NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT  2                                                                              5  3  1                                                                              2.4                                                                             1.5                                                                              NT NT NT                                                                              NT                              Tin                      2                                                                              2  1 2 1 1                                          Vanadium                NT                                                                              TR                                                                              NT 0.3                                                                             0.3                                                                             NT 420                                                                              417                                                                              TR                                                                              TR                              Zinc      1 3 TR 2 2 1  TR                                                                              1 TR TR                                                                              TR                                                                              TR  68                                                                               85                                                                               4                                                                               1                              Calcium   5 9 1  9 7 2  TR                                                                              3 TR TR                                                                              TR                                                                              TR 373                                                                              350                                                                              29                                                                              25                              Magnesium 1 1 TR 1 1 1  <1                                                                              1 <1 1 TR                                                                              TR 120                                                                              120                                                                              17                                                                              11                              Potassium   2           NT                                                                              TR                                                                              NT NT                                                                              NT                                                                              NT        5                                                                               3                              Sodium    NT                                                                              NT                                                                              NT NT                                                                              1 NT TR                                                                              TR                                                                              TR TR                                                                              TR                                                                              TR NT NT NT                                                                              NT                              Chlorides NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT                                                                              NT                                                                              NT NT NT NT                                                                              NT                              __________________________________________________________________________     Legend:                                                                       1 = Pretest                                                                   11 = TEST                                                                     111 = Post Test                                                               TR = Trace Result                                                             NT = No Test                                                                  Blank = None Detected                                                         Underlined = Notable Concentration Change                                

Table 5 presents the results of an analysis of the physical propertiesof the lubricant and the coker liquid products. It will be noted thatthe products are lower in sulfur and nitrogen content than the co-fedlubricant-slop.

Table 5 also presents the results of a physical analysis of eachhydrocarbon fraction produced by the instant process. The productcomponents are identified by their boiling points. The initial boilingpoint is determined for the slop lubricant and the different hydrocarbonfractions contained in the total feed both before the test and duringthe test. As the indicated amounts of liquid product distill-off, theboiling point of each fraction is determined. These values are reportedin Table 5. Light gasoline boils from 86° F. to 158° F., heavy gasolineboils from 221° F. to 408° F., light gas oil boils from 354° F. to 647°F. and heavy coker gas oil boils from 356° F. to 1001° F. The lubricantslop contains hydrocarbon fractions boiling within the range of each ofthese fractions and it can be concluded that each fraction distilledfrom the lubricant slop contributed to the total liquid product yield.It will also be noted that the sulfur and nitrogen content of the heavygasoline is within tolerable limits.

                                      TABLE 5                                     __________________________________________________________________________    PRODUCT PROPERTIES                                                                   LUBE                                                                              LT Gasoline                                                                           HVY Gasoline                                                                          LT Gas Oil                                                                            HVY Gas Oil                                       SLOP                                                                              Pre-Test                                                                           Test                                                                             Pre-Test                                                                           Test                                                                             Pre-Test                                                                           Test                                                                             Pre-Test                                                                           Test                                  __________________________________________________________________________    Dist. Data:                                                                   IBP    542 86   86 221  221                                                                              337  354                                                                              394  356                                    5%    649                         547  540                                   10%    687 100  103                                                                              241  240                                                                              432  431                                                                              603  602                                   20%    732                         657  657                                   30%    769                         696  686                                   50%    832 121  120                                                                              293  288                                                                              512  498                                                                              753  754                                   70%    895                         814  826                                   90%        154  146                                                                              375  362                                                                              625  585                                                                              908  951                                   95%                                950  --                                    EP     966 158  158                                                                              424  408                                                                              692  647                                                                              997  1001                                  Residue %                                                                            10  0    0.8                                                                              1.0  0.9                                                                              0.7  0.5                                                                              1.0  5.0                                   Loss % 1   7.9  1.1                                                                              0.5  0.5                                                                              0.2  0.2                                                                              1.0  1.0                                   Density                                                                              29.2                                                                              --   -- 52.8 53.7                                                                             33.8 34.7                                                                             19.1 21.4                                  (DEG API)                                                                     Vis 40 C.                                                                            47.7                                                                              --   -- --   -- --   -- --   --                                    Vis 100 C.                                                                           7.5 --   -- --   -- --   -- --   --                                    VI     111 --   -- --   -- --   -- --   --                                    Pour Pt (F.)                                                                         -10 --   -- --   -- --   -- --   --                                    Flash Pt (F.)                                                                        400 --   -- --   -- --   -- --   --                                    CCR wt %                                                                             0.5 --   -- --   -- --   -- --   --                                    Sulfur wt %                                                                          1.04                                                                              --   -- 0.5  0.44                                                                             --   -- --   --                                    Nitrogen wt %                                                                        0.04                                                                              --   -- --   -- --   -- --   --                                    Chlorides ppm                                                                        NT  --   -- --   -- --   -- --   --                                    __________________________________________________________________________     Legend:                                                                       EP = end product                                                              -- = not tested                                                               IBP = initial boiling point                                              

We claim:
 1. A process of used lubricating oil recycling whichcomprises:(a) introducing a coker feed to the coker furnace whichelevates the temperature of the coker feed to a temperature necessary tocarry-out delayed coking of the feed; (b) recycling a used lubricatingoil by adding the lubricating oil to the heated coker feed downstream ofthe coker furnace at a rate sufficient to maintain the temperature ofthe coker process stream at a temperature sufficient for delayed cokingand to prevent premature coking of the feed; and (c) carrying outdelayed coking of the feedstock in a coker drum from which coke andliquid coker products are removed.
 2. A process as described in claim 1in which the used lubricating oil is added to the coker feed at a rateup to about 10 volume percent based on the total volume of the feed. 3.A process as described in claim 1 in which the used lubricating oil ispreheated prior to addition to the heated coker feed in an independentcoker furnace.
 4. A process as described in claim 3 in which the usedlubricating oil is added to the delayed coker at a rate of more thanabout 3 volume percent based on the total volume of the feed.
 5. Aprocess as described in claim 3 in which the independent usedlubricating oil furnace outlet temperature is at most about 525° C.
 6. Aprocess as described in claim 1 in which the coker furnace outlettemperature ranges from about 400° C. to 525° C.
 7. A process asdescribed in claim 3 in which the heater outlet temperature is raisedfrom about 0.1° C. to 20° C. to maintain the coker drum temperature. 8.A process as described in claim 1 in which the coker drum inlettemperature ranges from about 400° C. to 550° C.
 9. A process asdescribed in claim 1 in which steam blowback is used to mix the usedlubricating oil with the process stream.
 10. A process as described inclaim 1 in which refinery sludge is added to a coker quench water in theprocess of removing the coke.
 11. A process of making liquid hydrocarbonfuels from a used lubricating oil in a delayed coking process whichcomprises:(a) heating a coker feedstock to an elevated cokingtemperature in a coker furnace; (b) injecting it with a used lubricatingoil heated to an elevated temperature in an independent used lubricatingoil furnace, whereby the heated used lubricating oil is a coker co-feed;(c) mixing the used lubricating oil with the process stream; and (d)carrying out delayed coking of the heated feedstock in a coker drum fromwhich solid and liquid coking products are removed, said liquid cokingproducts include hydrocarbons which are suitable as liquid hydrocarbonfuels.
 12. A process as described in claim 11 in which the independentused lubricating oil furnace outlet temperature is at most about 525° C.13. A process as described in claim 11 in which the heated usedlubricating oil is cofed into the process stream at an injection rate ofmore than about 3 volume percent based on the total volume of thefeedstock.
 14. A process as described in claim 11 in which the cokerfurnace outlet temperature ranges from about 400° C. to 550° C.
 15. Aprocess as described in claim 11 in which the heater outlet temperatureis raised about 0.1° C. to 20° C. to maintain coker drum temperature.16. A process as described in claim 11 in which the coker drum inlettemperature ranges from about 425° C. to 500° C.
 17. A process asdescribed in claim 11 in which steam blowback is used to mix thelubricating oil with the process steam.
 18. A process as described inclaim 11 which further comprises a step of quenching the hot coke.
 19. Aprocess of reclaiming a used lubricating oil in a delayed coking processcomprising(a) cofeeding the used lubricating oil containing largequantities of metal contaminants, heated in an independent furnace priorto cofeeding the oil into a heated coker feedstock process streamdownstream of the coker furnace; and (b) reclaiming the used lubricatingoil by carrying out delayed coking of the feedstock in a coker drum fromwhich useful liquid and solid coker products are removed.
 20. A processas described in claim 19 in which the outlet temperature of the usedlubricating oil independent furnace is at most about 525° C.
 21. Aprocess as described in claim 19 in which the heated used lubricatingoil is injected into the process stream at an injection rate of morethan about 3 volume percent based on the total volume of the feedstock.22. A process as described in claim 19 in which the coker furnace outlettemperature ranges from about 400° C. to 550° C.
 23. The process asdescribed in claim 18 in which a sludge is added to the coker as aquench liquid in the step of quenching the coke. .Iadd.
 24. In a delayedcoking process in which a delayed coking feedstock is subjected todelayed coking wherein the improvement comprises conducting delayedcoking of a mixture of a used lubricating oil and a delayed cokingfeedstock..Iaddend..Iadd.25. The delayed coking process of claim 24 inwhich the mixture of used lubricating oil and delayed coking feedstockcomprises up to 10 volume percent based on the total volume of the feedof used lubricating oil..Iaddend.